[Enzyme induction in Streptomyces hydrogenans. V. Characterization of testosterone-17 beta-dehydrogenase and its induction by steroids].

Testosterone 17beta-dehydrogenase can be enriched from Streptomyces hydrogenans. The enzyme dehydrogenizes testosterone with Km=13muM and estradiol-17beta with Km=21muM to the corresponding 17-ketoderivatives. NAD forms NADH with Km=125muM. The enzyme is strongly inhibited by androstandione and 17alpha-methyltestosterone. The Ki for 17alpha-methyltestosterone is 18muM. The enzyme activity increases with increasing pH up to alkali-mediated denaturation at about pH 10. The optimum temperature is at 45 degrees C. If Streptomyces hydrogenans is cultivated in the absence of steroids, the specific activity of testosterone 17beta-dehydrogenase in the cytosol of the microorganisms amounts to 10 mU/mg protein, and increases up to 10-fold if the cells are cultivated in the presence of certain steroids. Testosterone, alpha-dihydrotestosterone, beta-dihydrotestosterone, estradiol-17beta, and 17alpha-methyltestosterone are very effective inducers. Thus, for the first time, the ability of estradiol-17beta to induce an enzyme synthesis in a microorganism is shown. The steroid-dependent induction is inhibited by testosterone acetate and rifamycin SV. Cyproterone, however, does not decrease the testosterone-dependent enzyme induction of testosterone 17beta-dehydrogenase.